In this study, strength properties of concrete using steel-slag coarse aggregates such as electric-furnace oxidized-slag coarse-aggregate (EFG) or blast-furnace slag coarse-aggregate (BFG) were investigated. In addition, the cracking process when concrete using EFG and BFG had received compression loading was confirmed by acoustic emission (AE) techniques. As the result, the compressive strength of EFG concrete was 1.2 times as large as that of concrete using normal aggregates such as tight-sands crushed-stone (NG), river gravel (RG), and limestone crushed-stone (LG). BFG concrete had approximately the same compressive strength compared with concrete using normal aggregates. In the AE measurement result, the accumulation number of AE hits of EFG concrete increased with normal aggregate concrete. On the other hand, the accumulation number of AE hits of BFG concrete was increased notably from the early stress level. Therefore it was considered that a lot of destruction had occurred inside concrete from an early stage. From relation with stress level and improvement b (Ib) value, and RA value-average frequency(A-FRQ) relation, cracks that occurred inside BFG concrete were hard to progress even if more than stress level 40%. However, in the case of BFG concrete, cracks progressed easily from early stress level because of many voids which exist between coarse aggregate and mortar.
